The 48-year-old cried in the dock of Sydney's Downing Centre District Court where she sat beside her husband, 57, who has also pleaded guilty to sexually assaulting the boy.
The couple, who cannot be named for legal reasons, are facing sentencing for the offences against their son, which occurred between January and November 2009.
Some of the offences include streaming footage of the sex acts online.
The woman's lawyer Alex Morris cited a doctor's report that said her client suffered from a dependent personality disorder and referred to a "cocktail of medication to explain why she committed the offences".
"In the report (the doctor) refers to her describing herself feeling disgusted with herself and she realises she should have gone to the police but she didn't," Mr Morris said.
However, crown prosecutor Craig Everson said there was no evidence before the court to show the woman was taking any medication at the time of the offences.
Mr Everson conceded that the woman played a less significant role in the offending than her husband, who was "the instigator of the dysfunctional family unit".
"(The woman was) playing a role subordinate to that of her husband who was really the instigator and director of what was occurring," Mr Emerson said.
The court was told that the woman has begun divorce proceeding against her husband and that she "wants to have nothing to do with him".
She has pleaded guilty to sexual intercourse with her son and two counts of committing an act of indecency.
The man pleaded guilty to two counts of sexual intercourse with his son, two counts of committing an indecent act, using the nine-year-old for child pornographic purposes, indecently assaulting his son, possessing child pornography and using the internet to offend.
"There has been irreparable damage done to this young boy," Mr Emerson said.
Judge Peter Garling adjourned the matter for sentence on October 15.